Winter storage of lifepo4

[Flod]

My boat is hauled out and winterised for the coming cold period. We have like 4 months dec-mar below freezing. I have a 200ah winston lifepo4 pack in the boat. Just checked it and the cells are like 3.27v and soc is 55%. I have turned off the main circuit breakers and switched the load/charging relays off. Only thing that draw some current is the 123bms. Anything else I should do? I rather not take the pack out and haul it home.

[john61ct]

I would prefer to isolate the cells from BMS, not doing anything while in cold storage anyway.

And do not believe that -45°C, make sure the **inside** of the cells are well above freezing before allowing even a 0.05C charge rate.

Just how cold do you expect it to get there?

[Flod]

At most -15-20 degrees C. I won’t charge or use the batteries in the cold though.

[john61ct]

Should be OK. Maybe I'm ovrly cautious, but IMO if power's available, a low level heat source for peak cold overnights would not be a bad idea.

[rgleason]

This is the exact same situation I would have during the winter when and if I go with lifepo. So I thought, rather than move them home, perhaps use solarpv to warm up a resistance blanket during the day to keep the battery warmer at night and reduce thr low temps a little. The Boatyard allows no connections.

I dont know if it would work. Also if they loose charge, youd best be very careful about temps before charging them back up.

Some blanket insulation will also help to average out the temps

[Checkswrecks]

I'd increase the charge to 75-80% just in case there is a minor parasitic drain, disconnect the cables (BMS if external), clean the plastic case, and record the SOC once every month or so. It should be fine till Spring.

Obviously warm it to above freezing for more than a few hours if it does need a charge.

[rgleason]

Do lifepo when colder, use up some energy or do they just go into hybernation, with out movement of electrons?

Does anyone have experience with cold conditions and lifpo? How often should they be recharged in the winter?

Getting the boat and batteries up to proper temp in order to charge, might be difficult. What do others do?

Moving the battery might prove to be very disruptive, requiring some dismantling.

Hope you'll share your experience this winter

[john61ct]

Bare cells isolated have near zero cell discharge, and cold is ideal for long term storage, even years is fine without topping up. BMS or other parasitic loads are the dangerous wild card.

Personally I would check periodically, more frequently at first until confident, then scale back, eventually to say every other month.

A well insulated box with thermostatically controlled silicone heating pads at the bottom is the usual solution when needed.

If an easy water heating system was available then a hydronics solution might be easier.

Yes a long warm-up period is required to ensure the cell interiors match ambient inside the box.

Personally I'd rather design the bank from easily portable units.

There are also systems where the heating elements are part of the battery design.

[YANDINA]

A recent news article describes cryogenic freezing of Lithium batteries in liquid Nitrogen to immobilize them for transportation without the need for expensive protective packaging.

Tests after thawing showed no difference immediately however the ones that had been frozen had longer life.

[john61ct]

Very interesting!

In rereading my post above, realized this bit

Originally Posted by john61ct

Personally I'd rather design the bank from easily portable units.

may need clarifying.

Point being, just bring the packs inside to store them above ~10°C when it gets really freezing in their usual location(s).

In many contexts much more practical than heroic measures creating a dedicated temp-controlled insulated enclosure.